During the first two years of this research, the developmentally regulated plasma membrane proteins were defined and antibodies made to several of them. In addition a spontaneous cross reacting material (CRM) mutant with a nonfunctional carbohydrate binding protein (CBP) was isolated. Basically, then, the first two years of research served to define the membrane molecules which change during development and allowed preparation of antibodies and isolation of critical mutant strains. Renewal funds are now requested to build on this background to make structure-function correlations during development.